"A" pillars basically are the sides of the front window frame. As for the splice approach, sure you can make it work but be sure to have inner supports welded in place from the inside cab wall to the floor and to the dash to retain the cab configuration. You will also want to have your doors in place when you set the new roof on to get your gaps and alignment set. It may turn out just find but it will still be fun to watch. As for the flanged connection across the rear panel, that may not work well. What I did was weld in a flat bar stock to the inside surface and used that to make the welds to. It provided strength and additional metal to weld to. There may be a pic or two of that on my picture trail album. If not let me know and I can send you some pics of how I did the rear panel transplant.
As for transplanting just the windows, someone probably has done that but to me that would almost be more fraught with danger....ROTFALMAO
As for cab rust, I had to replace all four corners plus cowls and floor. In my mind it is easier to leave the big peices together and fix the small ones.
Others will probably chime in here and either agree or disagree with my suggestions. There are many different methods of resurrecting these cabs. Some good, some not so. Whichever you choose, it will be a challenge. Good luck. Drop me a line if I can help.
